1. Field of the Invention
This invention relates to a lighting device suitable for a vehicle which has various lighting devices (namely, light fittings) such as a head lights or lamps.
2. Description of the Related Art
A conventional lighting device of this type is disclosed in, for example, the U.S. Pat. No. 4,958,263 (corresponding to the Japanese Unexamined Patent Publication (Kokai Tokkyo Koho) Official Gazette No. H2-172102). In this conventional lighting device, light emitted from a light source is incident on an end of a bundle of optical fibers. This incident light is guided through the bundle of optical fibers. Then, light outputted from the other end of the bundle of optical fibers is emitted forward of a vehicle through an optical transmission device.
In this conventional lighting device, however, the optical transmission device has a complex structure and as a consequence this lighting device cannot have a compact structure. A compact structure cannot be achieved since the transverse section of the end of the bundle of optical fibers of the device has a rectangular shape the vertical side of which is shorter than the horizontal side, such that the (transverse) luminous intensity distribution curve of light emitted from the device is shaped like a rectangle, the vertical side of which is shorter than the horizontal side thereof (namely, the vertical side is relatively short and the horizontal side is relatively long). Further, even if the traverse section of the end of the bundle of optical fibers is shaped like a circle and the light outputted from the bundle of optical fibers is made to be transmitted through two aspherical cylindrical lenses, the axes of which intersect orthogonally, in such a manner that the (transverse) luminous intensity distribution curve of the emitted light is shaped like an ellipse which has a minor axis in the vertical direction and a major axis in the horizontal direction, the conventional lighting device cannot sufficiently carry out an essential function of illumination. Namely, the head lamp cannot illuminate forward of the vehicle to a distant place. Further, in the conventional lighting system, there is air in an optical path thereof along the direction in which the light propagates. Therefore, the conventional lighting device has another drawback in that the utilization factor of the emitted light used for direct illumination to the emitted light which is not used for direct illumination, is low. The present invention is created to eliminate the above described drawbacks of the conventional lighting device.
It is, accordingly, an object of the present invention to provide a lighting device for use in a vehicle, which device has a simple construction and is compact and can perform the essential function thereof and have a high utilization factor.